A solid polymer-type fuel cell is a fuel cell in a form where a solid polymer electrolyte is sandwiched between an anode and a cathode and, by supplying a fuel to the anode and oxygen or air to the cathode, oxygen is reduced at the cathode to generate electricity. As the fuel, hydrogen, methanol or the like is mainly used.
On the anode and the cathode, an electrode catalyst layer composed of an electrode catalyst and an electrolyte called “ionomer” is formed. For the formation of such an electrode catalyst layer, conventionally, an electrode catalyst layer-forming ink comprising a volatile solvent such as an alcohol as a dispersion medium is used along with a catalyst and an electrolyte solution. As the electrode catalyst, conventionally a carbon-based catalyst in which noble metal particles are supported on carbon particles is used.
As an electrode catalyst layer-forming ink comprising such a carbon-based electrode catalyst, for example, JP-A-2004-95553 (Patent Literature 1) discloses, as a working example, an ink prepared by stirring and mixing 10 g of a platinum-supported carbon catalyst (Pt: 20 wt %) with 40 g of an electrolyte solution, which is a 5 wt %-NAFION (registered trademark) solution (manufactured by DuPont, solvent: normal propyl alcohol), using a dispersion apparatus.
In addition, JP-A-H9-501535 (Patent Literature 2) discloses, as a working example, an ink prepared from 2.6 mg of NAFION solution (manufactured by DuPont (prepared from 5% by weight of NAFION, 50% by weight of isopropyl alcohol, 25% by weight of methanol and 20% by weight of water)), 390 mg of 1-methoxy-2-propanol, 2 ml of isopropyl alcohol and 487.9 mg of a catalyst (manufactured by Precious Metals Corporation) having 20% platinum on a VULCAN (registered trademark) carbon support.
Meanwhile, in WO2009/017011 (Patent Literature 3) and the like, metal oxide-based electrode catalysts are disclosed as platinum-alternative catalysts. Moreover, in JP-A-2013-30470 and JP-A-2013-116458 (Patent Literatures 4 and 5), catalyst electrodes of a type in which noble metal particles are supported on metal oxide particles are disclosed. In the working examples of these literatures, catalyst inks for cathode are prepared using an aqueous solution obtained by mixing 25 ml of water and 25 ml of propyl alcohol.